Display devices have employed cathode-ray tubes (CRT) to display images. However, various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and electro-luminescent display (ELD) devices, are currently being developed as substitutes for the CRT. Among these various types of flat panel displays, LCD devices have advantages of thin profile and low power consumption, but have disadvantages of using a backlight unit because they are non-luminescent display devices. However, as organic electroluminescent display (OELD) devices are self-luminescent display devices, they are operated at low voltages and have a thin profile. Further, the OELD devices have advantages of fast response time, high brightness and wide viewing angles.
As shown in FIG. 1, a pixel of the related art OELD device is connected to a gate line S, a data line D and a power line VDD. The pixel includes a switching thin film transistor N1, a driving thin film transistor N2, a capacitor C and a organic light emitting diode OLED.
A gate electrode of the switching thin film transistor N1 is connected to the gate line S, and a source electrode of the switching thin film transistor N1 is connected to the data line D. One electrode of the capacitor C is connected to the drain electrode of the switching thin film transistor N1, and the other electrode of the capacitor C is connected to a ground terminal (GND). A drain electrode of the driving thin film transistor N2 is connected to a cathode of the organic emitting diode OLED, a gate electrode of the driving thin film transistor N2 is connected to the drain electrode of the switching thin film transistor N1, and a source electrode of the driving thin film transistor N2 is connected to the ground terminal (GND).
FIG. 2 is a waveform view of a gate signal, a data signal and a power signal applied to the pixel of FIG. 1.A gate signal having a high or low level VGH or VGL is applied to the switching thin film transistor N1 through the gate line S. When the high level VGH is applied, the switching thin film transistor N1 is turned on. When the switching thin film transistor N1 is turned on, a data signal is stored in the capacitor C and the driving thin film transistor N2 is turned on. Accordingly, a current flows on the driving thin film transistor N2 and the organic emitting diode OLED emits light. The stored data signal determines an amount of a current flowing on the driving thin film transistor N2, and the amount of the current determines light intensity of the organic emitting diode OLED.
When the related art OELD device is used as a high resolution display device, the number of signal lines and driving ICs needed increases. When the OELD device is used as a high resolution and small size display device, installation space of the components required maybe insufficient.